1. Field of the Invention
The invention relates to image forming method and apparatus for forming an image onto a recording material.
2. Related Background Art
Hitherto, there has been known a method whereby an image forming apparatus is activated and, after completion of a warm-up, a specific pattern is formed on an image holding member, a density of the pattern on the image holding member is read and is fed back to image forming conditions such as a gamma correction or calibration and the like, thereby improving a stability of an image quality.
Further, in the case where image forming characteristics are changed due to an environmental fluctuation or the like, the specific pattern is again formed on the image holding member in accordance with an environmental fluctuation amount, a density of the pattern on the image holding member is read and is fed back to the image forming conditions such as gamma correction or calibration and the like, thereby stabilizing an image quality.
In the above conventional method, however, in the case where the image forming apparatus is used for a long time, there occurs a case where the read density of the pattern on the image holding member doesn't coincide with a density of the image which was actually printed out.
For example, since a cleaning blade for cleaning a transfer residual toner is come into contact with the image holding member and the image holding member is rubbed for a long time, the surface of the image holding member becomes rough and the relation between a deposition amount of the toner and a reflected light amount changes from an initial state.
There is, consequently, a drawback such that when the image forming apparatus which was used for a long time is fed back to the image forming conditions by using the density data converted by an initial density conversion parameter, the optimum image cannot be obtained.
On the other hand, in the above conventional method, since no consideration is made to a deterioration of the maximum image density of the image forming apparatus, in the case where the maximum image density output is decreased due to an influence by a durability fluctuation or the like, there is a drawback such that even if a gamma characteristic is corrected, a gradation of the image deteriorates in a region of a high image density.
In the above conventional method, since a gradation characteristic of the image forming apparatus is not linear (particularly, highlight), when data between density data is interpolated by an approximate expression, the resultant density differs from the actual density. There is, consequently, a drawback such that when the density is fed back to the image forming conditions by using the gradation data, the optimum image is not obtained.
Further, according to the above conventional method, when a uniform density is outputted to the whole surface of the recording member in the image forming apparatus, in the case where a jump of a density appears due to a charging variation by a dirt of a charging device, the density changes in dependence on the location even in case of the same density output. There is a drawback such that in the above state, if the density is fed back to the image forming conditions by using the gradation data, the optimum image is not obtained.